Pellicle container kit

ABSTRACT

A pellicle container kit is proposed in which the corner clips to bind together the cover and tray of the pellicle container are made of a resin having a durometer hardness of from D58 to D64 and preferably they are made of either polyurethane resin or polyethylene resin.

PRIORITY CLAIMED

The present non-provisional application claims priority, as per Paris Convention, from Japanese Application No. 2010-192310 filed on Aug. 30, 2010, the disclosure of which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

A set of inventions are herein disclosed in relation to a container case capable of withholding a generation of friction power arising from frictional sliding between matters; in particular, the inventions relate to a pellicle container kit including a corner clip for binding a pellicle container case for containing a pellicle, which is a dust fender for a reticle and a photomask used in the photolithography process to manufacture semiconductor devices.

BACKGROUND TECHNOLOGY

In recent years, the requirement for higher density and higher integration in semiconductor devices has pushed the progress for ever higher resolution of patterns in the photolithography process. This trend was accompanied by inadvertent incidences wherein, for example, even an infinitesimal foreign particle adhering to the photomask surface becomes a cause for a defect in the transferred pattern, so that in order to prevent such particles from adhering to the photomask, it has become essential that a pellicle is put on the photomask.

Such a pellicle is composed mainly of a metallic frame and a transparent membrane, namely a pellicle film, which is stretched and bonded over one of two annular faces of the frame, and when the pellicle is attached to the photomask by the other annular face, the exposure light which is set to focus on the photomask face fails to focus on the transparent membrane owing to the distance between the membrane and the photomask face, thus it is possible for a relatively large foreign particle to land on the transparent membrane, for such a particle fails to shed its shadow on the photomask face.

However, if a foreign matter sticks to the inner side of the pellicle film which faces the hollow of the pellicle frame or to an inner wall of the metallic frame during the manufacturing or transportation of the pellicle, it is possible that the foreign matter falls onto the photomask when in use, and this can cause a defect in the resulting semiconductor chip, so that it is common practice that during the transportation of the pellicle the pellicle is contained in a plastic case which is designed to maintain the cleanliness of the pellicle.

FIG. 1 is an illustration of a conventional pellicle container case. As shown, a pellicle 4 is placed on a tray 2, and a cover 3 is placed over these, whereupon the cover 3 secures the pellicle by the edges of the film-bearing annular face of the pellicle frame (Publication-in-patent 1). However, this is not sufficient to stop the relative movements between the tray 2 and the cover 3 so that a number of corner clips 5 are used to stop such movements.

FIG. 2 shows a conventional corner clip. This corner clip is formed with a penetrating hole 5 h into which one of four corners of the pellicle container case 1 is inserted, and the inner walls of the hollow clip are formed with a press member 5 m and a protruding stopper member 5 u adapted to hook on a cover periphery rib 3 u (Publication-in-patent 2).

In order to securely clip the corners of the pellicle container case 1, the corner clip 5 needs to withstand the resistive reaction force of the container case 1, so that the clip 5 is made of a material which is more resilient than the materials that are used to make the pellicle container case such as ABS resin, acrylic resin, polycarbonate resin, polyethylene, polystyrene, polypropylene, and the like. On account of this resiliency, however, when the corner clip 5 is pressed on a corner of the pellicle container case 1 for engagement, there occurs a friction between the press member 5 m and the protruding stopper member 5 u of the corner clip 5 on one hand and the pellicle container case 1 on the other, and a problem of creation of abrasion powder is experienced.

PRIOR PUBLICATIONS Publications-in-IP [Publication-in-patent 1] Japanese Utility Model Application Publication H1 (1989)-120148

-   [Publication-in-patent 2] Japanese Registered Utility Model     Publication No. 3042696

SUMMARY OF THE INVENTION Problems the Invention Seeks to Solve

The inventor of this application studied the above-mentioned problem intensively and found that it is possible to stop the creation of the abrasion powder which is caused when the corner clip 5 is slid on a corner of the pellicle container case 1 by means of making the corner clip 5 out of a material that is a resin of a durometer hardness of D58 to D64—hence reached to the present invention.

Therefore, it is the object of the present invention to provide a plastic corner clip that can be used in combination with a pellicle container case without generation of the abrasion powder from friction during the setting of the corner clip 5 to a corner of the pellicle container case 1.

Incidentally, there are several scales of durometer, used for materials with different properties. The two most common scales, using slightly different measurement systems, are the ASTM D2240 type A and type D scales, which are commonly learned by a person skilled in the present art. The A scale is for softer plastics, while the D scale is for harder ones. A higher value represents a harder material. It is the type D scale that is used in the present invention.

Means to Solve the Problem

Hence, the present invention proposes a set of pellicle container kit including a corner clip used in combination with a pellicle container case, the latter being composed of a tray on which a pellicle is laid and a cover which engages with the tray in a manner such that a hollow is made between them to contain the entirety of the pellicle, and the improvement lies in that the corner clip is made of a resin having a durometer hardness of D58 to D64. According to the invention, preferable resins to make the clip are urethane resin and polyethylene resin for the reason of relatively high plasticity, and best mode resin is polyethylene set to have a density of from 0.94 g/cm³ to 0.95 g/cm³.

FUNCTION OF THE INVENTION

When the inventive corner clip is used in combination with the pellicle container case, the latter which is composed of a tray adapted to provide a seat for the pellicle and a cover adapted to engage with the tray in a manner such that a hollow is made to contain the entirety of the pellicle, it is possible to stop the creation of the abrasion powder which is otherwise liable to occur as a result of the friction between the conventional corner clip and the pellicle container case.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a set of drawings to show how the corner clips are used on the pellicle container case and drawing (A) is an a top view, drawing (B) is a side view, and drawing (C) is a cross sectional view of the pellicle container kit cut and seen as suggested by the arrows A, A and the broken line in drawing (A).

FIG. 2 is a set of drawings showing the fabrication of the container clip for the pellicle container case.

EMBODIMENTS OF THE INVENTION

With reference to FIG. 1, the manner in which the pellicle container kit is used will be explained. In the drawings the reference numeral 1 is a pellicle container case, 2 is a tray, 2 m is a bottom face of an outskirts portion of the tray, 3 is a cover, 3 u is an outskirts rib of the cover, 4 is a pellicle, 5 is a clip, 5 a is an inward opening of the clip, and 5 b is an outward opening of the clip, 5 h is a penetrating hole, 5 o is an outer rib, 5 i is an inner rib, 5 u is a stopper member, and 5 m is a press member.

As is clearly known from FIG. 1, a pellicle container case is designed to work such that, after fitting the pellicle 4 on the tray 2 in a predetermined position as guided by pins, the cover 3 is fitted to the tray, also in a predetermined position, to thereby effect a detachable engagement between the tray 2 and the cover 3. On this occasion, the pellicle 4 contained inside is rendered immobile as the cover 3 comes in contact with the edges of the film-bearing annular face of the pellicle frame [see drawing (C)].

The inventive corner clip 5 for the pellicle container case is designed to lock the case containing the pellicle 4 from inadvertently opening during transportation, and this clip is preferably put to all the corners of the case as shown in drawing (A) of FIG. 1, which shows a completely assembled pellicle container kit.

As shown in FIG. 2, the corner clip has a penetrating hole 5 h, which is capable of receiving a corner of the pellicle container case, consisting of respective corners of the tray 2 and cover 3. An inner ceiling wall of the hollow clip is formed with a stopper member 5 u adapted to hook with a cover periphery rib 3 u so as to prevent detachment of the clip; an inner bottom wall of the hollow clip is formed with a press member 5 m adapted to oppress the bottom face 2 m of the outskirts portion of the tray so as to prevent slipping of the tray relative to the cover that may be caused by shocks.

The corner clip according to the present invention is made of a resin having a durometer hardness of D52 or harder. Such a resin material has an appropriate amount of resiliency so that it is possible to deform the corner clip between fingers and to thereby facilitate its smooth engagement with the pellicle container without causing substantial friction between the corner clip and the container case—hence subduing creation of abrasion powder. In the present invention, it is preferable that the corner clip is made of polyethylene or polyurethane resin for the reason of their good plasticity suitable for injection molding.

The hardness of the resin material to make the corner clip, according to the present invention, is designed to be D58 or harder in terms of durometer hardness, for although it is a fact that the softer the clip the easier it is to fix the clip to the pellicle container case, it is a more important fact that the softer the clip the easier it is for the clip to give off abrasion powder. On the other hand, if the clip is too hard, it may impart damages to the pellicle case thereby causing production of abrasion powder, so that the resin for the clip should not be harder than D64. This preferable range seems to correspond to 0.94 g/cm³ to 0.95 g/cm³ in terms of the density of the resin to make the clip.

We will now explain the invention by way of Examples and Comparative Examples, but the invention is not limited to the Examples.

Examples 1 and 2 and Comparative Examples 1 and 2

The pellicle container cases used in the examples are the same as the one shown in FIG. 1 in semblance; therefore, the pellicle container kit of the present invention consists of a tray 2 to provide a seat for the pellicle 4, a cover 3 to cover up and engage with the tray 2, and corner clips 5 each having a penetrating hole 5 h to be penetrated by the respective corner of the pellicle container case 1 as the latter is in the assembled form of the tray 2 and the cover 3.

The corner clips used in the examples are the same as the ones shown in FIG. 2, and therefore, each corner clip 5 has: the penetrating hole 5 h to be penetrated by a corner of the pellicle container case as an assembly of the tray 2 and the cover 3; the stopper member 5 u formed in the inner ceiling wall of the clip 5 adapted to hook on the periphery rib 3 u of the cover 3 so as to prevent detachment of the corner clip 5; and the press member 5 m formed in the bottom wall of the clip 5 adapted to oppress the bottom face 2 m of the outskirts portion of the tray 2 so as to prevent slipping of the tray relative to the cover.

The tray 2, the cover 3, and the clip 5 were all made by injection molding, and were made of ABS static protective resin or PMMA antistatic resin or polyethylene resin.

Six specimens of corner clip were made of polyethylene resin having different durometer hardness, namely D46, D52, D58, D64, D70, D78 (respectively having a density of 0.92, 0.93, 0.94, 0.95, 0.96, 0.97 g/cm³). Tests were conducted on these specimens.

The test was commenced by bringing a tray 2, a cover 3, and a corner clip 5 tailored for a pellicle measuring 149 mm×122 mm×6.3 mm into a clean room of class 1000, where they were subjected to ultrasonic cleaning in a surface-active agent and then in pure water.

Thereafter, the parts were transferred to a clean room of class 1. Then, the pellicle 4 was placed on the tray 2 and then the cover 3 was set on the tray 2, and the cover 3 and the tray 2 were exposed to a 300 lux spot lamp light and the foreign matters adhering to the surfaces at one of the corners were counted with the naked eye.

Now, the four corners of the container were clipped with the respective corner clips 5, whereby the pellicle 4 was securely contained in the case 1.

Next, with hands wearing clean gloves, the corner clip 5 which was put to that corner where the foreign matters had been counted was removed from the corner and again put back on the corner, and this removal was repeated ten times; finally, in a dark room, the cover 3 and the tray 2 were again exposed to a 300 lux spot lamp light and the foreign matters adhering to the surfaces of said corner were counted with the naked eye. The result was as shown in Table 1.

TABLE 1 Properties incremental of corner clips number of foreign durometer density particles hardness (g/cm³) cover tray Comparative Example 1 D46 0.92 24 7 Comparative Example 2 D52 0.93 9 3 Example 1 D58 0.94 0 0 Example 2 D64 0.95 0 0 Comparative Example 3 D70 0.96 4 1 Comparative Example 4 D78 0.97 8 5

In the cases of the corner clips 5 of Comparative Examples 1 and 2 of which the durometer hardness was D52 or softer, significant creation of clip abrasion powder was observed, which is thought attributable to the friction between the stopper member 5 u and the cover periphery rib 3 u and that between the press member 5 m and the bottom face 2 m of the outskirts portion of the tray 2 on account of the substantial softness of the clip material. On the other hand, in the cases of the corner clips 5 of Comparative Examples 3 and 4 of which the durometer hardness was greater than D64, some creation of clip abrasion powder was observed, which is thought caused by the hard friction between stopper member 5 u and the cover periphery rib 3 u and that between the press member 5 m and the bottom face 2 m of the outskirts portion of the tray 2 attributable to the increased hardness of the clip material. As opposed to these results, in the case of the corner clips 5 of the present invention, of which the durometer hardness was from D58 to D64, there was observed no creation of abrasion powder, and this was thought to be by virtue of the moderate hardness of the clip materials.

POSSIBILITY OF INDUSTRIAL USEFULNESS

By using the corner clips of the present invention, it is possible to minimize the amount of abrasion powder that is created when the corner clips are slid on the corners of the pellicle container case, so that this invention is a useful contribution to the photolithography industry.

EXPLANATION OF REFERENCE NUMERALS

-   1: pellicle container case -   2: tray -   2 m: bottom face of the outskirts portion of the tray 2 -   3: cover -   3 u: cover periphery rib -   4: pellicle -   5: corner clip -   5 a: inward opening of the clip -   5 b: outward opening of the clip -   5 h: penetrating hole -   5 o: outer rib -   5 i: inner rib -   5 u: stopper member -   5 m: press member 

What is claimed is:
 1. A pellicle container kit comprising a tray, a cover, and a number of resin corner clips, wherein the tray and the cover form, when coupled together, a pellicle container with corners, and the corner clips are adapted to fit on the respective corners of the pellicle container to lock said coupling, and improvement consists in that a durometer hardness of the corner clip is from D58 to D64.
 2. The pellicle container kit as claimed in claim 1 wherein said corner clips are made of a material selected from urethane resin and polyethylene resin.
 3. The pellicle container kit as claimed in claim 1 wherein said corner clips are made of polyethylene resin having a density of from 0.94 g/cm³ to 0.95 g/cm³. 